<!DOCTYPE html>
<html>
<head>
<meta charset="UTF-8">
<script>

function boom() {
    CSS.supports('');

    var style = document.createElement("style");
    var tn = document.createTextNode("* { border: var(--b); }");
    style.appendChild(tn);
    document.body.appendChild(style);
}

</script>
</head>
<body onload="boom();"></body>
</html>
